Process of manufacturing alumina.



No. 706,553; Patented Aug. I2, 1902.

" C. M. HALL.

PROCESS OF MANUFACTURING ALUMlNA (Application filed Aug. 10, 1901.)

WITNESSES Tm: mm: germs co. morouma, WASNINGTON. c.

UNITED ST TE PATENT OFFICE,

CHARLES M. HALL, OF NIAGARA FALLS, NEW YORK.

PROCESS OF MANUFACTURING ALUMINA.

SPECIFICATION forming. part of Letters Iatent No. 706,553, dated August12, 1902. Application filed August 10, 190i. Serial No- 71,639. (Nospecimens.)

To aJZ 1077/0111 it may concern:

Be it known that I, CHARLES M. HALL,0f Niagara Falls, Niagara county,New Y ork, have invented anew and useful Process'of ManufacturingAlumina, of which the follow-1 ing is a full, clear, and exactdescription, ref crence being had to the accompanying (new, ings.

Figure 1 shows in vertical section apparatus suitable for the practiceof myinvention, and Fig. 2 is a horizontal section on the line II II ofFig. 1. f In the process described in'rny priorpat-f ent,N0. 677,207,forpurifying bauxite orsimi-j lar material containing alumina, includingthe silicates of aluminium, it is important to: reduce as much aspossible the consumption of electric power. It is also desirable toreduce the evolution of carbonic monoxid gas, for the reason that ifmuch gas is given off it is apt to blow portions of the material out ofthe furnace and to render'the operation difficult to control. One methodof accomplishing these two objects is described in my prior patent,No.677,208, in which aluminium, pure or alloyed, is used as a reducingagent for the impurities of the bauxite. I have now discover'eda cheaperand more economical method of accomplishing these results namely, topartially reduce the material by means of carbon and a high degreeofheat,

generated by the electric current before it isput into the zone offusion in the electric furnace. In order to accomplish this object, Imix the bauxite or other impure oxid of aluminium (in which term Iinclude the silicates) with an amount of carbonproper to reduce the ironoxid, silica, and titanic acid, and, if the iron is deficient, withsufficient iron or other heavy metal to alloy with the silicon andtitanium to be reduced, and I then heat the mixture in an electricfurnace to a high temperature,but below the melting-point of alumina. Bythis means the iron oxid contained in the bauxite is substantiallyreduced to metallic iron, and the silica, and generally the titanicacid,see1ns to be partially red uced. With some grades of bauxite thematerial is fritted together-4 a, it seems to undergo incipient fusion.An advantage of thus fritting the material instead of completely fusingit is that at the temperature at which such "fused by means of anelectric current, and

while fused the reduction of the impurities is completed, andthe reducediron, silicon,

and titaniumagglomerate into fused masses,

which at the end of the process can readily be separated from thepurified alumina.

For the preliminary treatment of the bauxite anysuitable form ofelectric furnace may be used; but I prefer to use one in which adifiused heat is supplied to the mass, for it .is not desirable in'thisoperation to fuse the bauxite or to use a source of heat concen tratedat any point, as if this is done the same difficulties of evolution ofgas which it is the purpose of this invention to avoid are apt to occur.

I may use aform of electric furnace having a large carbon core, eithergranular or solid, with the material piled around it, similar to thatused in the well-known carborundum furnaces, and in such case thecurrent should be so regulated in this core as to heat the charge to betreated to the best working temperature-that is, to the point at whichthe iron is reduced-and the silica and, in some cases, titanic acid arereduced partially or wholly but without substantial fusion of thebauxite. The best and most economical 'means of accomplishing the resultof this preliminary treatment of the bauxite I have found to be to pilethe material to be treated-that is the raw bauxite mixed with carbon andwith iron, if necessary-around the zone of fusion in the same electricfurnace, and, in fact, forming a part of the same furnace in which thefinal operation of fusion and purification of a previously-treatedamount of bauxite takes place. In this way I utilize the waste heat ofthe fusion process, and the heat given off by the fused charge after thefusion and separation is complete to heat up and partially reducewithout fusion a mass of material which is subsequently treated in thesame furnace or in another furnace in the zone of fusion, a new mass ofmaterial being piled around it and treated as before. The apparatuswhich I use in this operation consists, preferably, as shown in carbonand bauxite, together with extra iron,

if necessary. The fusion is started in the interior of the inner shellby bringing the hanging electrodesin contact with the carbon base,turning on the current, slightly raising the hanging electrodes toforman arc, and piling around them previously-treated bauxite for fusionand purification. The inner iron shell had best be perforated, as at 7,so as to allow whatever gas there is to escape on all sides, and thereshould be openings 8 for gas in the outer shell. This gas is at anextremely high temperature as it leaves the neighborhood of I theelectrodes and gives up its heat to the the surrounding bauxite.

material through which it passes, heating the unreduced charge in theouter portion of the furnace and to some extent the material around theelectrode which is subsequently to be fused. As the process continues,more and more'of the charge in the zone of fusion is fused, and more isadded as the mass of melted material rises higher and higher. Thismelted material gives ofi' a portion of its heat to the fresh'chargesurrounding the zone of fusion, raising its temperature and causing apartial reduction of the impurities. The process continues until as muchmaterial has been fused 'in the inner space as the furnace can safelyhold, or as much as the power used can keep in fusion at one time, forit is not desirable to continue the process until a portion of thecharge which has once been melted becomes solidified by attempting tomelt too much. The current is then taken off and the hanging electrodesare withdrawn and the furnace is allowed to stand. The liquid bauxiteand the iron alloy in the zone of fusion gradually cool and solidify,giving off their heat to This'is an important part of the operation whenit is conducted under the best conditions, for the reason that itutilizes a considerable .portion of the otherwise wasted heat energy ofthe fused alumina, which on account of the well-known veryhighmelting-point of alumina must be atan extremely high temperature.This heat is largelytransmitted into the charge surrounding the zone offusion and causes the reaction of the carbon there, with the iron oxidpresent, and to a greater or less extent with the silica or'silica andtitanic acid. At the same time it dries out the last traces of water,which it is almost impossible to remove in an ordinary calciningoperation. When the operation is worked. on a fairly large scale, I havefound it desirable after the current is taken off to allow the furnaceto stand for days and even two or three weeks.

'As bauxite is a very poor conductor of heat,

' and the outer portions of it continue to grow hot for a considerabletime. When the furnace has been allowed to stand for a sufficient timeit is pulled down, and the unfused material, much of which has undergoneincipient fusion or, at least, is partially fritted together, is takenout and broken up more or less and used in the. zone of fusion in thesubsequent operation, fresh mixture of bauxite and carbon being used, asabove described, toform the outer portions of the furnace and to absorband utilize the heat of the charge, which would otherwise be wasted.

When the furnace is pulled down and the partially-reduced material istaken out, it is desirable to expose it as little as possible to the airwhile in the heated condition, for the reason that the reduced ironpresent being in a finely-divided form is liable to reoxidize, and thesame is true of the silicon and titanium so far as they are reduced.

I have worked my process successfully with a current of aboutfive-hundred-horse power at approximately fifty bolts and seven thousandtwo hundred amperes,the charge being placed upon a carbon slab sevenfeet in diameter and fourteen inches thick, and a group of fivesuspended carbons being employed to constitute the electrode; but thesemay be varied by the skilled operator.

I claim 1. The method herein described of puritying bauxite or otherimpure oxid of aluminium, which consists in heating the same inadmixture with a reducing agent by means of an electric current withoutsubstantial fusion, thereby reducing the contained impuritiesin whole orin part, removing the mass so treated and afterward fusing it in anelectric furnace and causing the impurities to agglomerate;substantially as described.

2. The method herein described of puritying bauxite or other impure oxidof aluminium, which consists in heating and fritting the same inadmixture with a reducing agent by means of an electric current, withoutsubstantial fusion, reducing thereby the contained impurities in wholeor in part, removing the mass so treated and afterward fusing it in anelectric furnace and causing the reduced impurities to agglomerate;substantially as described.

3. The method herein described of purifying bauxite or other impure oxidof aluminium, which consists in surrounding a mass containing such oxidwith a mixture of like oxid and carbon, subjecting it to heat generatedby an electric current, fusing it thereby and causing the impuritiesthereof to unite in a fused alloy, and by the waste heat so developedeffecting a reduction, in whole or in part, of the surrounding mixturewithout IIO substantial fusion of such mixture, then removing thepurified central mass, and subsequently fusing such surrounding mixtureto effect the removal of its impurities; substantially as described.

4. The method herein described of purifying bauxite or other impure oxidof aluminium,which consists in surrounding a mass containing such oxidwith a mixture of like oxid and carbon, subjecting it to heat generatedby an electric current, fusing it thereby and causing the impuritiesthereof to unite in a fused alloy, allowing said mass to cool slowly,and by the waste heat so developed effecting a reduction, in whole or inpart, of the sur rounding mixture without substantial fusion of suchmixture, then removing the purified central mass,- and subsequentlyfusing such surrounding mixture to effect the removal of its impurities;substantially asdescribed.

5. The method herein described of purifying bauxite or other impure oxidof aluminium, which consists in surrounding a mass containing such oxidwith a mixture of like oxid and carbon, subjecting it to heat generatedby an electric current, fusing it thereby my hand.

CHARLES M. HALL. Witnesses:

K. M. FLAHERTY, T. J. BosrWIoK.

